Outboard motor problems

check your full cap is letting air in easily. Try running with it loose.

Plugs maylook ok, first thing I would try 2 new spark plugs if its missing underload as they are generaly the first to break down under load.

Had a similar problem twice with cars.

Breaking down under load.

New plugs didnt fix it.

Found problem when opened bonnet in the dark.

Plug leads were shorting back to a connection for a heater hose.

Replaced with solid wire leads instead of carbon filled ones and had no more trouble.

Commondores had the same trouble.
Had a VS that would hiccup and miss and wouldnt know what gear it wanted to be in.

New plug leads fixed it as well.

If you sharply bend carbon filled leads you can create a gap which will cause breakdown under load.

Might be worth a look.

Hi, First thing is to replace the spark plugs, these come with a resistor spark plugs and they can break down under load. So replace them with a non resistor version, ie; b7hs-10 instead of br7hs-10, if that does not work try fresh fuel. Do not bother to replace the leads as they are part of the ignition coil and its expensive. and rarely fail. The only thing it could be is the cdi unit (switch box) But on this model we hardly ever have to replace them.

Hi

No there will be no difference in performance. In some parts of the world ie; North America and also, Europe they must by law use resistor spark plugs.

Jon, by no means an expert on O/B motors but if all else fails, give the carb bowl a sharp tap or two.

Cheers.....Lionel.

Jon,
Had one of those OB's for quite a few years myself.
The above advice is spot on re the plugs and leads.

What i did find is this, because you run 2 stroke with oil in it thru the fuel line from Tank to OB, when not using it - the fuel will evaporate out of the hose past the ball bearing type seals at each end. This leaves the 2 stroke oil behind in the hose, to form a hard buildup.

This happens especially up north in the heat & the more times this happens - the more oil crud builds up inside the hose.

Eventually - there comes a time when you either kink the fuel hose or put the fuel tank down on top of it - causing the hose to deform from round.

When this happens - the hardened dried up oil inside the fuel hose comes away from the inside wall of the hose in small hard black flakes.

These flakes go into the fuel bowl.

Under acceleration - load - they get sucked into the high & mid speed jets, blocking them - leaning out the mix, and causing misfires.

Often when you slow to idle - they will wash out of the top of the jet (being flat and hard they don't seem to actually permanently block the jet) and swirl around in the fuel inside the carby bowl, - allowing the OB to idle fine.

The best practice was to drain the fuel bowl of fuel and get the flakes of hard 2 stroke oil out of the bowl.

Its something to think about when you have a 2 stroke and use it in remote creeks in crock country etc - something as simple as treading on the fueo line or kinking it can loosen that black oil residue thats hardened in the hose.

ONE way to avoid this is to fit one of those plastic Ryco type fuel filters into the fuel line, after the priming bulb & just before the actual connection to the outboard!

That will help ensure the paper cartridge filter traps any such flakes of hardened oil.

Now.

With that out the way.

There's another possibility - and that's water in the fuel.

Again humid places like monsoonal north will get water condensate inside your fuel tank overnight and thus into your carby.

Solution?

Add a Racor brand water separating filter into the back of the boat and run your fuel line from the tank to the separating filter then to the outboard.

That last solution solves all the p[reevious possibilities - yet so few boaters do it.

Mainly thoise of us who run fishing charters and need a RELIABLE outboard go to the trouble.

The rest spend their time on forums like this - asking what went wrong.

IMHO - it should be illegal to take any boat to sea, without a Racor water separating filter in the fuel line.

Then again who knows - it might be something else entirely! ;o)

Cheers

G'day happy travellers, you may have a developing overheating problem which causes the spark plugs to break down under load. The most likely cause of the overheating is a perished water pump impeller. I once had a 10hp Tohatsu and was very impressed by its simplicity and robustness and easy access for engine maintenance. If you are not mechanically handy, I would advise you have a qualified person replace the water pump impeller.

Hi

It possibly could be some rubbish in the float bowl, but he described a misfire not a surge as would be if there was some rubbish in the float bowl.Also don't forget there is only one carby on the 25/30 hp lightweight Mercs, so in theory the motor should stall because a lack of fuel, then you would be able to restart when the boat levelled out. We see these motors in at work all the time with this problem and 90 times out of a 100 its just the plugs. NGK are not as good as people think they are or at least in outboard motors. It also may help I I run a large regional marine workshop and have been in the game for 30 years. One thing more to check, is where the leads go into the coil, make sure the grommets are not damaged in any way, because the rear cowl latch can sometimes damage them as inexperienced people put the motor cover on.

Putting in fresh fuel is the first step. I even once had problems after refueling and the problem went away after I tried a fresh tank of fuel from another servicie station. Fuel does go "flat" within weeks and two strokes must have fresh fuel. No need to throw the fuel away it can be mixed bit by bit with a tank of fresh fuel once the problem is eliminated.

I had an old Suzuki 20HP carbi fed that generated a similar fuel starvation problem.
It was caused by the carbi float valve not opening fuully, and at cruising speed the fuel coming into the carbi did not quite meet the needs, and the float bowl wou;ld run dry after a half hours constant use.
If you have electronic ignition, you can probably ignore this.
Cheers

Being a two cylinder engine and getting full throttle without load it could be the CDI unit has failed.

This happened to my 40 hp 4 cylinder engine, I had full throttle without load EG: bottom two cylinders were firing, but under load I was two cylinders short.

So it might pay to run you engine and see if one of the cylinders stays cold while the other gets hot.